This radical discovery could turn semiconductor manufacture inside out

How to "grow" self-assembling semiconductors, atomic layer by atomic layer
November 30, 2012

a, Au (gold) agglomerate formation; b, Au agglomerate size sorting using a differential mobility analyzer; c, Au agglomerate compaction into spherical particles in a furnace; d, nanowire growth; e, nanowire deposition (credit: Lars Samuelson et al./Lund University)

A completely new method of manufacturing the smallest structures in electronics could make their manufacture thousands of times quicker, allowing for cheaper semiconductors.

Instead of starting from a silicon wafer or other substrate, the idea is to grow gallium arsenide semiconductor structures from freely suspended nanoparticles of gold in a flowing gas. Semiconductor nanowires are key building blocks for the next generation of light-emitting diodes, solar cells, and batteries, according to Lund University researchers.

Behind the discovery is Lars Samuelson, Professor of Semiconductor Physics at Lund University, Sweden, and head of the University’s Nanometer Structure Consortium. He believes the technology will be ready for commercialization in two to four years. A prototype for solar cells is expected to be completed in two years.

“When I first suggested the idea of getting rid of the substrate, people around me said ‘you’re out of your mind, Lars; that would never work.’ When we tested the principle in one of our converted ovens at 400°C, the results were better than we could have dreamed of,” he says.

Nanowire (credit: Lars Samuelson et al./Lund University)

“The basic idea was to let nanoparticles of gold serve as a substrate from which the gallium arsenide semiconductors grow. This means that the accepted concepts really were turned upside down!”

Since then, the technology has been refined, patents have been obtained and further studies have been conducted. In the article in Nature, the researchers show how the growth can be controlled using temperature, time and the size of the gold nanoparticles.

Recently, they have also built a prototype machine with a specially built oven. Using a series of ovens, the researchers expect to be able to “bake” the nanowires, as the structures are called, and thereby develop multiple variants, such as p-n diodes. A further advantage of the technology is avoiding the cost of expensive semiconductor wafers.

“In addition, the process is not only extremely quick, it is also continuous. Traditional manufacture of substrates is batch-based and is therefore much more time-consuming,” adds  Samuelson.

Aerotaxy

SEM image showing deposited nanowires on a Si substrate (credit: Lars Samuelson et al./Lund University)

At the moment, the researchers are working to develop a good method to capture the nanowires and make them self-assemble in an ordered manner on a specific surface. This could be glass, steel or another material suited to the purpose. The reason why no one has tested this method before, in the view of Professor Samuelson, is that today’s method is so basic and obvious. Such things tend to be difficult to question.

However, the Lund researchers have a head start, thanks to their parallel research based on an innovative method in the manufacture of nanowires on semiconductor wafers, known as epitaxy — so the researchers have chosen to call the new method aerotaxy. Instead of sculpting structures out of silicon or another semiconductor material, the structures are instead allowed to develop, atomic layer by atomic layer, through controlled self-organization.

The breakthrough for these semiconductor structures came in 2002 and research on them is primarily carried out at Lund, Berkeley and Harvard universities.

The Lund researchers specialize in developing the physical and electrical properties of the wires, which helps create better and more energy-saving solar cells, LEDs, batteries and other electrical equipment that is now an integrated part of our lives.